The present invention relates generally to indexing apparatus and more particularly to drive systems for use in conjunction with such indexing apparatus so as to provide extremely smooth jerk-free acceleration and deceleration of the driven apparatus.
Indexing apparatus of various types have long been in use in conjunction with various types of manufacturing and assembly operations in order to advance workpieces between work stations as well as into and out of various types of machinery. Numerous types of drive systems have been developed over the years in order to accomplish this work transfer operation in a rapid and efficient manner. Typically, such drive systems have employed different combinations of barrel cams, bell cranks, lever arms, or scotch yoke connections and the like. Typically such drive systems must be able to provide periods of dwell at both beginning and ends of the operational cycle with intermediate periods of acceleration/deceleration and possibly a period of constant velocity.
It is highly desirable to provide drive systems for such indexing apparatus which are able to smoothly reciprocate the workpieces into and out of the work stations without subjecting either the workpiece or the associated apparatus to shocks or jerk resulting from sudden acceleration or deceleration from or to a stationary position. This is particularly important with regard to such indexing apparatus which is designed for use in assembly operations wherein the jerk may dislodge parts being assembled although it is desirable to avoid such jerk in all applications because of the adverse effect resulting from subjecting the entire drive train to the stress and strain associated therewith.
It should be noted that as used herein the term "jerk" is defined as the third derivative of displacement with respect to time or the second derivative of velocity with respect to time or the first derivative of acceleration with respect to time.
In addition to reducing or eliminating jerk in such indexing apparatus both at the beginning and end of operational cycles it is also desirable to design such apparatus to be able to reciprocate the workpiece into and out of the work station as rapidly as possible because this transfer represents lost production time. Also, in order to avoid excessive downtime as well as high maintenance costs, it is highly desirable to design such apparatus as simply as possible with a minimum number of moving parts. Coupled with the desire to maintain the design as simple as possible while still accommodating the other operational aspects required is the desirability to enable the apparatus to be easily fabricated at relatively low cost without sacrificing reliability. While previous indexing drive arrangements have been able to achieve differing measures of success in meeting the above conflicting objectives, none of them have been totally effective in providing a completely acceptable indexing drive assembly.
The present invention, however, provides a substantially improved drive system which utilizes a cam and cam follower arrangement specifically designed to provide extremely smooth transition between dwell and acceleration periods which are substantially jerk free. The cam surfaces are designed so as to be easily machined in flat stock thereby substantially reducing the manufacturing costs of the drive system from those employing barrel cams which require extremely costly specialized machining techniques to machine a cam groove along the cylindrical periphery thereof. Additionally, the arrangement of the system is such that the cam surfaces and cam follower operate to insure continuous precise control of the apparatus throughout the full operational cycle of the indexing apparatus. Additionally, because the cam and cam followers are arranged so as to provide extremely smooth jerk free work transfer, the apparatus is not subject to the repetitive stresses and strains associated with jerk movement and therefore offers the advantage of substantially reduce downtime due to equipment failure. The cam grooves are designed so that while jerk is substantially reduced or totally eliminated, the transfer operation is still accomplished within a minimum amount of time because of the ability to provide rapidly increasing rate of acceleration.
Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings.